We will study the mechanisms which control B cell responses to antigen in the mouse. These studies will include experiments to determine how products of the H-2 major histocompatibility complex express in B cells and macrophages control the interactions of these cells with helper T cells. Using antisera directed against various B cell surface components (Ia, Ig, ala-1) we will determine which components are important in B cell responses to various mitogens and antigens. Finally, we will attempt to determine the mechanism by which Con A induced T cells inactivate a non-specific helper T cell factor.